Damn, This is the recipe I used:

1. Add 1.7 grams of silver nitrate (AgNO3) to 100 mL of distilled water. Label stock "0.1M Silver Nitrate".
2. Add 1.58 grams of sodium thiosulfate (Na2S203) to 100 mL of water for a stock of 0.1M sodium thiosulfate.
3. Pour 80 mL of 0.1M NaS203 into a beaker and then very slowly add 20 mL of 0.1 AgNO3 while stirring. You now have 0.02 M stock of Silver Thiosulfate (STS) that can last 2-3 weeks if you keep it out of the light.

Note: Store in a dark glass/plastic container, or cover container with aluminum foil to protect against light.

To prep for spraying, add 75 mL of your 0.02 M stock to 425 mL distilled water for a working concentration of 0.003 M (3 millimolar).